Additives can be mixed into the waste while still in
the ground (often referred to as “in situ”). This usually
involves drilling holes using cranes with large mixers or
augers, which both inject the additives underground and
mix them with the waste. The number of holes needed
depends on the size of the augers and the contaminated
area. Dozens of holes may need to be drilled. When
the waste is shallow enough, the contaminated soil
or waste is excavated and additives are mixed with it
above ground (often referred to as “ex situ”). The waste
is either mixed using backhoes and front end loaders
or placed in machines called “pug mills.” Pug mills can
grind and mix materials at the same time.